Three years after the BP oil spill, the US Coast Guard says only 95 miles of coastline remain to be cleaned. But critics say the full extent of the damage is not yet known, especially in Louisiana, where oil is deep in the coastal environment.

Tar balls lie mixed with shells on the beach in Gulf Shores, Ala., in this June 11 file photo. Three years after the BP oil spill in the Gulf of Mexico, the petroleum giant and the Coast Guard say extraordinary cleanup operations in Alabama, Florida, and Mississippi are done. Louisiana officials want the effort to continue.

Dave Martin/AP/File

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(Updated at 9 a.m. Aug. 16.)

With about 100 miles of coastline remaining to clean up following the Gulf of Mexico oil spill three years ago, the states most impacted by the disaster say it is too soon to stop, because the environmental damage is ongoing.

“The response should end when conditions on the ground dictate such actions. We’re not anywhere close right now,” says Garret Graves, chair of the Coastal Protection and Restoration Authority of Louisiana (CPRA), a state agency leading hurricane protection and ecosystem restoration.

When the Deepwater Horizon oil rig exploded in April 2010, killing 11 people and releasing 205 million gallons of crude into the ocean for 111 days, it started a long and complicated process to determine who is responsible, and how much – and for how long – they would dedicate to the cleanup process, which most agree will never be fully complete.

To date, cleanup efforts have been overseen by the US Coast Guard, which reported in June that the shorelines of Florida, Mississippi and Alabama are complete, leaving most of Louisiana, where patrols remain actively looking for oil. According to the Guard, there are 90 responders currently working in Louisiana, compared with the 19,000 people who were dispatched in July 2010 to comb the beaches, marshes, and barrier islands searching for tarballs, sheen, and oil swept as much as 10 feet below coastal shorelines.

Those efforts have been disappointing, because locating submerged oil is often tedious, labor-intensive work that does not guarantee successful results. According to the Coast Guard, of the 2.9 million pounds of sand, shells and water dredged to date, the vast majority – 85 percent – did not contain oil.

On Tuesday, the Coast Guard released a report that says just 95 miles of coastline are left to clean. However, the report did not project exactly how long it will take to complete the process.

“We don’t have an end date,” says Chief Petty Officer Pat Howell, the Louisiana branch director for the Coast Guard’s Gulf Coast Incident Management Team, which is heading the response in that state.

“Once there is an agreement is made that clean is clean, that’s when we will depart. I’m sure there will be a lot of data to back that up and to say we’re ready for the next phase of response," he adds.

That next phase “depends on the public to be our eyes” Officer Howell says. Instead of an active and ongoing search, the Coast Guard will dispatch crews only if they receive a tip on their hotline of an oil sighting and only if a forensics investigation proves the oil can be traced back to the Deepwater Horizon. If that is the case, BP, the oil giant largely responsible for the disaster, will pay the bill.

Because Louisiana’s delicate coastline of marshes and reefs received the most oil, the state has been fighting to prevent a winding down of the cleanup effort and says that a more comprehensive approach is needed to mitigate oil that remains deeply embedded into the coastal environment.

“Louisiana has made a very strong case why they don’t want their state taken out of response. They probably have a fear that it’s going to get harder and harder to get anyone to come in and respond because it becomes harder and harder to prove the chemical signature of the material over time,” says David Muth, director of the Mississippi River Delta Restoration Program for the National Wildlife Federation (NWF).

Environmental groups are also worried because they say the oil-soaked environment continues to damage wildlife reproduction cycles, which will receive less attention once the recovery effort ends. A NWF report, released in April, uses data from the National Oceanic and Atmospheric Administration (NOAA) to show that dolphin deaths are above average since the spill and that infant dolphins were found dead at six times the average in January and February. Killifish, sea turtles, and coral species are also badly damaged, the report says.

“The idea that just because BP discontinues their active response that [the coast] is cleaned up is untrue,” says Mr. Muth.

The state says the recovery efforts so far have primarily focused on beaches, a problem since the majority of Louisiana’s coast consists of wetlands, which makes beach remediation largely unnecessary.

“BP has refused to do any type of proactive oil reconnaissance effort” in Louisiana,” says Mr. Graves, who is leading Louisiana’s efforts to restore its wetlands. “They are refusing to go find the oil in areas adjacent to our wetlands, yet they walked and drove entirely shorelines in Mississippi, Alabama, and Florida for years – where relatively little oil shored.”

BP spokesman Jason Ryan characterizes Graves's assessment as "misleading." "We have proactively carried out a comprehensive effort to locate and remove residual oil from the Louisiana shoreline," he says. [Editor's note:This paragraph was added to the original story once BP returned the reporter's phone call.]

The state is also wary of the relationship between BP and the Coast Guard. Howell says that while his agency “has federal oversight to oversee all operations,” the shoreline crews are BP contractors hired largely from Danos, a Louisiana company whose relationship with the company dates back to 2009, one year before the spill.

“We have shoreline treatment regulations they have to follow,” he says. “The Coast Guard is out there making sure the recommendations are followed.”

Graves disagrees, saying “BP runs the show” in the recovery on the ground.

“It has been fascinating and frustrating to experience a private company dictating federal agency actions – a modern day case of Stockholm Syndrome. We have seen nothing that anyone other than BP is supervising their cleanup contractors,” he says.

However, one of the difficulties from treating oil in a wetlands environment is that exposure could cause more damage than letting it natural degrade over time, says Frank Galgano, an expert on coastline ecology at Villanova University outside Philadelphia.

“If it never gets exposed again, it’s just going to decay,” Dr. Galgano says. The fragility of the wetlands means “it’s not a very responsive or resilient environment,” so active dredging, and other recovery techniques, means the possibility of creating damage.

“There’s always unintended consequences when you change the natural system,” he says. While walking away from an active recovery phase may “sound like someone is trying to get out of their obligation, but maybe not. Sometimes the cure is worse than the disease.”

While BP has paid about $14 billion in response activities and settlement payouts to damages unrelated to restoration, a civil trial enters its second of three phases in September that will ultimately determine how much the company is on the hook to pay out in environmental penalties. The civil damages from the upcoming trial are estimated at about $20 billion.

"It's highly unlikely we are now going to enter into some sort of detailed settlement discussions. Unfortunately, some of the circumstances that are happening today suggest that it may be in the best interests of our shareholders now to play it long,” he said, according to Dow Jones Newswires in July.

In the meantime, the Gulf Coast Ecosystem Restoration Council, which includes the governors of all five coastal states, will meet in New Orleans on Aug. 28 to vote on a restoration plan that was finalized in May. The council will oversee the spending of 60 percent of any BP oil spill fines, 30 percent of which will be administered according to the plan.